That's true Graham, and also why we don't speak about
'Most General Unifier', but about (for anonymous nodes)
'does that thing have this thing at Least in Common'
(which is indeed asymmetric)
--
Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo
Graham Klyne <GK@NineByNine.org>@w3.org on 2001-07-03 02:08:51 PM
Sent by: w3c-rdfcore-wg-request@w3.org
To: jos.deroo.jd@belgium.agfa.com
cc: fmanola@mitre.org, connolly@w3.org, phayes@ai.uwf.edu,
w3c-rdfcore-wg@w3.org
Subject: query and unification
Hmmm... my take is that querying is asymmetric, but unification is symmetric:
(query Q D) != (query D Q)
but
(unify E1 E2) == (unify E2 E1)
Maybe query is a special case of unification in which only one expression
contains a variable to be substituted?
#g
--
At 01:08 AM 6/30/01 +0100, jos.deroo.jd@belgium.agfa.com wrote:
>that query thing is an interesting idea!
>when we try to unify 2 anonymous nodes it is actually
>like a query of one node against the other node
>(the latter node looking like an in-line set of statements)
>so the former one is existentially quantified
>whereas the latter one is universally quantified
>(and subjects match immediately (we use null's for them))
>and so everybody is right
>
>--
>Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/